Bone conduction hearing-aid



Apri 20, 1937. H. LIEBER 2,077,425

l BONE CONDUCTION HEARING AID Original Filed Deo. 24, 1932 2 Sh-eet's-Sheet 1 HTTOHEY April 20, 1937. H. HEBER 2,077,425,

BONE CONDUCT-10N HEARING AID original Filed Dec. 24, 1952 2 sheets-sheet 2 Q5/.1l l1.3 '82 111)' 8,9 in

mvfmon Hugo beber g M Fm .Q TTORNEY 1 Claim.

` Rossum JUN 2 0 |944 Patented Apr. 20, 1937 UNITEDl sTTEs PATENT OFFICE Hugo Lieber, New York, N. Y., assignor, by mesne assignments, to Lieber Patents Corporation, New York, N. Y., a corporation of New ,York

Application December 24, 1932, Serial No. 648,733 B ,enewed February 28, 1934 This invention relates to bone conduction hearing-aids, and it has among its objects an improved bone conduction receiver of small size and light Weight suitable for inconspicuous wear by the user and able to impart to the bone structure of va hard of hearing person the vibratory energy required for inducing hearing in his auditory nerve center.

The foregoing and other objects of the invention will be best understood from the following description, reference being made to the accompanying drawings, in which Fig. 1 is a view of the vibrator element illustrating how a bone conduction receiver of the invention may be held against the bone structure of the upper portion of the spinal column of a person hardofvhearing;

Fig. 2 is a circuit diagram of a hearing-aid device;

Fig. 3 is a vertical sectional view through the bone conductionv receiver along line 3 -3 of Fig. 4;

Fig. 4 is a vertical sectional view of the receiver along line 4-4` of Fig. 3;

6 Fig. 5 is a horizontal sectional view through -the 'receiver along line 5 5 of Fig. 4;

Fig;y 6 is a top view and Fig. 7 is a cross sectional view of the pole plate of theJ receiver;.

Figs. 8 and 9` are vertical sectional views similar to Fig. 3 of the center portion of a receiver embodying modifications, of the inventioni Fig. 10 is a view of a modiiled formof a boney conduction receiver ofthe invention as carried lon the head of a person; Fig. 11 is a verticalsectional view through the receiver of Fig. 10 along line I of Fig. 12;

Fig. 12 is a vertical sectional view along line |2|2 of Pg. -11;

Fig. 13 is an elevational view of the vibrator casing of Fig. 11, .with the cover and the vibrating diaphragm removed, along line |3-I3 of Fig. l1;

Fig. 14 is a transverse sectional detail view along line |4|4 ofFlg. 11;

Fig. 15 is a transverse sectional detail view al^ng line |5|5 of Fig. 11; and

Fig.; 16 is a view.A similar to Fig. 15 of a modifled construction. r Although it has been known for many years "0 that a large percentage of persons with impaired hearing have satisfactory interior hearing organs and that they are able to hear well by bone' conduction, prior bone conduction` receivers proved 55 impractical because they were all large and cumbersome and could not be made small enough y for inconspicuous wear by the user.

induce satisfactory hearing, andyet small and light enough to permit its inconspicuous wear on the personof the user.

Fig. 1 illustrates a hard-of-hearing person havinga bone conduction receiver 2| o'f the invention held pressed against a spinal columnbone by means of a light harness of flexible straps 22, the receiver being connected through al flexible double conductor cord 23 with the associated elements, in accordance with the diagram of Fig. 2. 'I'he complete hearing-aid comprises a transmitter microphone 24 connected through a cutout switch 25 in series with a battery 26 and actuating coil 21 of a microphone amplifier 28, the microphone 29 of which is connected through switch 25 in series with battery 26 and rheostat 30 to the actuating coil 3| of the bone conduction receiver 2| as in similar air conduction hearingaids.

The bone conduction receiver 2| is shown in detail in Figs. 3 to 'land comprises a casing 32 within which is mounted an electromagnetic vibrator core structure comprising a central core 34 `surrounded by the actuating coil 3| and two L-shaped permanent magnets 38 so as to produce with the pole plate 4|), shown in detail in Figs. 6 and 7, a flux in the annular gap between the core and the pole plate.

Mounted above the pole platewithi'n the casing opening isa diaphragm unit 5| comprising a. circular resilient sheet-metal diaphragm 52 held radially tensioned by a tension ring 53. The tension ring may be, for instance, made from a 'split ring of larger diameter compressed to the diameter of the diaphragm and soldered to the edge thereof so that under the action of the forces tending to restore the ring to its original position, a uniform radial tension is applied to the diaphragm.

To the underside of the diaphragm is secured', as by soldering, a flat circular armature 54 of soft iron. 'Ihe lower surface 55 of the armature 54 is parallel to the pole faces of the central core member 34 and the pole plate 40 and is spaced therefrom by a small gap 56 to provide a path for the permanent iiux of the magnets 38 and of the induced ux -of coil 3|. The diaphragm unit it held rmly in place within the casing by means Of a locking ring 56 which is screwed in within the threaded upper end of the interior casing wall, thin washers`51 serving to properly space the diaphragm unit with respect to thet pole faces $5 .and 49. f

5 The top of the casing is closed by a cover 60 mounted on an external threaded portion of the casing, and a lock nut ring 63 serves to lock the cover-.inthe desired operating position. The central portionof the cover 60 has a central cylindrical opening 65 for guiding a. contact button 66 mounted on a rod 61 extending from the center of the armature 54. The contact button 66 may be mounted in place before inserting the cover by l placing it with its central hole over the upper 16 projection of the rod 61 and soldering the two together at the top end, a thin cap 68, of a nonoxidizlng material, for instance, gold, being soldered over the top of the junction to form the exterior contact surface of the button 66.

20 The outer side of the central enlargement 64 of the cover 60 forms a supporting surface 69 around the contact button 66. When the vibrator is in released condition, the outer surface 68 of the contact button projects slightly above the supporting surface 69. of the casing cover, as

shown in Fig. 4.l Y (J l If the bone conduction vibratorl isin released condition, that is, not held pressed with the contact button 66 against the bone structure to which' vibrations are to be imparted, and the vibrator is connected to the operating circuit as shown in Fig. 2, only a permanent flux is induced in the.

gaps 56 between the pole faces of the magnet core and the opposite armature face, the flux passing between the inner pole face 35 through the short gap to the armature 54 and then radially through the armature to the outer periphery thereof, and therefrom back through the gap to the cuter pole face '49 of the pole plate 40 and therethrough to 40 the opposite poles of the L-shaped magnets, a part of the flux being also induced by the steady current owing through the coil Y 3| from the battery 26. This-ux will tend to pull the armature 54 towards the pole faces underneath, but the diaphragm 52 is made sumciently stiff to oppose this magnetic pull and to keep it in the position where the contact button 66 projects above the supporting surface 69, as shown in Fig. 4. On pressing the vibrator against the body, the contact surface 68 is pressed inwardly into the opening of the cover until the outerl contact surface 68 of the button lies flush with the supporting surface 69, as shown in Fig. 3, the body portion being indicated by line 16. This brings 55 the armature nearer to the pole pieces, decreasing the air gap. Y

If sound waves impinge upon the transmitter microphone 24, producgig oscillatory currents in the circuit of coil '3L/corresponding oscillatory .60 iluxes are induced in the magnet core and these 70 latter to vibrate. These mechanicalvibrations of the contact button ,66 conform to the sound os- `cillations impinging upon the transmitting microphone 64 and by impartingthese mechanical v'ibrations to the hearing-inducing bone structure of a person, corresponding sounds are induced in the nerve center of the person.

y The amount of vibratory power that can be transmitted by a vibrator of this type to the bone structure depends on the area of the pole face 5 of the gap and on the gap length. -The larger the active area of the gap and the smaller the length of the gap, the more mechanical power can" be transmitted by the vibrator. vIf the device is to be small and inconspicuous, the pole area must natu- 10 rally be kept small. The only way then open to make such vibrator develop a substantial amount of undistorted mechanical power is to decrease the gap between the pole faces and the opposite' armature surface. This brings, however, about 15 serious difficulties which have prevented in the past the construction of small size inconspicuous vibrators for bone conduction hearing-aids.

In a magnet system with a movable diaphragm 4disposed close Ato the pole face, the magnetic flux 20 between the opposite surfaces exercises on these surfaces a very strong attracting force, and tries to bring the diaphragm into contact with the pole faces. This action is particularly strong d uring the operation of the device when the coil is 25 energized and increases the magnetic force, and especially so when current pulsations materially increase the flux. If under such conditions, the gap between the armature and the pole faces is very small, there will be reached a point at which 30 the attractive force of the magnet will pull down the armature 4into contact with it, rendering the vibrator inoperative. There exists thus a freezing zone in the immediate neighborhood oi the pole faces from which the armature must be positively 35 kept out' in order to prevent inoperativeness of the vibrator unit. 'I'he fact that in pressing the contact button 66 against the bone structure in devices, as shown in Figs. 3 and 4, thegap between the armature and the pole faces is decreased, 40 greatly increases these difficulties, and has been in the past a great obstacle in making small practical bone conduction receivers. In trying to the past, and yet avoid to a large extent the difficulties due to freezing. The diaphragm unit is 55 so constructed and mountedv that with the actuating coil i I energized, the armature will beheld in a position at which there is a substantial gap between the core pole faces 49 and 35 and the armature face so that the magnetic flux in the 60 gap will under no condition reach a value causing the armature to be pulled into contact with the pole face. A vibratoremploying such large gap during operation would, however, have to `be too large in size. in order to develop power for 05 imparting to the bone structure suiiicient vibration to induce audible sounds in the auditory never center.

' In accordance with the invention, I provide a much smaller normal operating gap by arrang- .-0 ing the contactbutton 66 to project above the surroundingsupporting surface 69 of the casing when in released position as shown in Fig. 4, and

to be pushed lntotecasi, .when it is pressed with thel button surface, against the bone structure, till it reaches a position where the outer contact surface of the button is substantially flush with the adjacent supporting surface of the casing. This inward/motion of the button is accompanied by a corresponding motion of the diaphragm till the armature reaches a predetermined operating distance from the pole faces beyond which it cannot be pushed' by the butto'n. This' operating gap is made only little larger than the freezing gap distance so that the armature may vibrate in the region close to the gapzone in which it would be caused to freeze, but, nevertheless, stay outside the freezing zone and vis brate under the action of the normal flux ucl5 tuations induced by the coil. By thus bringing the armature toa position wherenthe gap is larger than the freezing zone and yet not too large, the vibrator is able to develop relatively large power in a structure small enough to be inconspicuously warm on the body of the user. y In the use of such vibrators, sound vibrations stronger than normal will often occur. In such cases thecurrent flowing through the actuating coil 3| may momentarily become so large as to increase the ux in the gapgto a value at which the armature vibrating nearthe border of the normal freezing zone will be pulled over by the increased flux and become frozen notwithstanding that under normal operation no such pull' over will occur. Such momentary freezing of the armature is quite frequent if the operating gap of the armature is made close tothe freezing zone, and very little advantage would be gained by choosing such small gaps because once the armature is frozen to the pole faces; the circuit must be cut off 'and the vibrator shaken to get the armature out of the` freezing position.

In accordance with the invention, this difficulty is overcome to a'substantial extent by preventing permanent freezing of the armature to the pole faces in the`presence of lexcessive magnetic fluxes in the gap, and instantaneousrestoration of the vibrator to the non-freezing condition upon the disappearance and passing of excessive momentary magnetic fluxes. This is effected by attaching thin flat spacers13, as by soldering, to the pole face 49 of the pole plate 39, these spacers being of Ynon-magnetic material, for V1nstance, brass, and stopping the downward move- 50 ment of the armature at a distance before it contacts with the pole faces. With such spacers, a large magnetic force produced by a speech current impulse, although it mLght cause momentary ulling in of the armature into the freezing zone, will not beable to produce any permanent freezing-of the armature',` and the armature will be free to return to normal operating position.k

. The vibrator of the invention is thus characterized by two special spacingarrangements, one governing the' positioning of the armature duringtoperation to secure normal operation with'a relatively small gap subject to occasional freezing, but able 'to produce sufliciently powerful mechanical vibrations with a small structure, and the other preventing a momentary freezing action from impairing the continuity and readiness of operation of the device. stop fixing the normal operatingposition of the armature at a spacing lying just beyondl the freez- 70 ing zone. efficient operation is obtained with a small structure. By the provision of a second stopwmaintaining a minimum gapbetween the opposite pole surfaces in case of an occasional nf'reezing, the close spacing is deprived of its By the provision of a danger without materially affecting the continuity ofthe operation of the vibrator unit.

In the practical construction of a vibrator of the invention, satisfactory results may be obtained by limiting the inward movement of. the

contact button 66 so that in the position to which the button is brought by compressing it against the body, the operating gap between the armature surface and the pole faces of the magnet core is about 3 to 4 mils. The stop members 13 should be of a thickness of about 1 to 2 mils and prevent the armature from coming near the pole faces closer than that distance. A vibratorl made to operate with such gap spacing and constructed in the way shown in Figs. 3 to 7 may be made to have an outside diameter of about millimeters and a height of about 25 millimeters. being thus inconspicuous and readily adapted for wear on the bodyof the user.

Exact adjustment of the normal operating position at which the contact surface of the` button is flush with the surrounding supporting surface of the cover may be effected by turning the cover one way or another by means of ridge 62, the nut 63 serving to lock the cover in adjusted position. Al'nstead of securing the armature stops 13 to the pole face 49 of the pole plate 40, these stops may be secured to the under-surface of the armature 54 as shown at 16 in Fig. 8, the stops being kattached by soldering, for instance, and

having a thickness of about 1 to 2 mils as before.

In the modification shown in Fig. 9, the hole 85 within the casing is provided on its inner side with an inward projection 11 which performs the same function as the spacers 13 and 16 in the when released, in the position indicated by dotted lines 68' and on pressing the button against the body, the button surface is lowered to the position fiush with the supporting surface 61 of the casing cover, thereby bringing the armature into the normaloperating position lying close beyond the normal freezing zone. Direct contact and permanent freezing of the armature 54 to tge pole faces 35 and 49 is positively prevented y the projection 11 stopping the bottom edgeA of the button 66, so that a definite minimum spacing of about 1 to 2 mils is assured between the armature 54 and the pole faces, thereby securing momentary defreezingon disappearance of they excessive flux conditions that produce freezing.

In Figs. 10 to|15 is shown a modified form of a .boneconduction vibrator of the invention, which similar to the construction shown'in Figs. 3 and 4. The core member 84 and' the permanent magnets 85v are held together and are clamped to the' pole plate by means of a clamping strip 81, which has its ends 88 overlapping and secured by screws 89 to the underside of the pole plate 86. 'I'he pole plate has a central opening 90 and a pole face coplanar with the pole facerof the l central core member 84'.. Slots 98' ae provided in the pole plate to prevent eddy currents.

'constructions of Figs. 3 and.8, respectively. As

bushing 95 having its head contacting, by means l of a spring 96, with the metallic magnetic core strap 81 and therethrough making connection to the other terminal of the actuating coil 9|.

`A resilient, thin diaphragm strip 96, of steel,

for instance; is secured at its ends to the ends of 15 pole` plate 89 by means of screws 91 between clamping blocks 98 and adjusting blocks 99, the

latter blocks being slotted to permit their shifting in longitudinal direction to adjust the active length of the diaphragm strip 96. To the center 20 of the diaphragm 98 is secured, as by soldering, an armature plate |0| overlapping the pole face |02 of the central core and the pole face |03 oi' the pole plate and providing a by-pass for the Y flux between the two, like in the iirst vibrator. A

25 vibrator button |05 is secured, by means of a rod |06 to the armature |0| of the diaphragm unit, so that upon vibration of the latter by reason of uctuating iiuxes induced by oscillatory currents in coil 9|, corresponding mechanical vi- 30 brations are imparted to the vibrator button |05. 'I'he vibrator button is soldered to the end of the rod |08 and is provided with a cap 01, the external surface of which is designed to engage the bone structure,to whichv the vibration is to be 35 transmitted. The magnetic cores 04, 85, 86 with the diaphragm unit and the vibrator button may be assmbled as a unit outside' of the casing and then placed within the casing, as shown in Figs.

11 and 12, and clamped in positionby placing the cover i I0 thereover and securing the ends thereof by bolts to the casing ends, as shown in In the center of the casing cover ||0 is provided an enlarged portion ||4 having a threaded 45 opening H5 within which is threadedly mounted a collar H8 having a central opening fitting around the vibrator button and permitting longitudinal movement of the latter within the opening. Theiianged outer portion ||1 ofthe collar forms a supporting surface surrounding the contact button similar to the supporting surface 69 of the rst vibrator.v The position of the supporting surface I1 and the normal operating gap of the amature may be readily adjusted by 55 turning thec'ollar IIB in the threaded opening i to the right or the left, andthe collar may be locked in any desired position by locking nut H8. 'Ihe vibrator unit is held on an extension F20 of the head band 80 by means of a metallic clamp |2l having its ends secured to the rear side'of the casing and constituting a sleeve into which the slightly-bent, spatula-like member |20 ts.

'Ihe normal adjustment of tthe collar ||6 is 65 so ma'de that, with the actuating coil 9| enersized, and the vibrator in released position, the

contact button'projects slightly abo`ve the supporting surface I|1 of the; collar, as'shown in Fig. 12,35; Upon applying the instrument to the 70 bone structure by means of the head band, the

pressurez.- exerted by the .head band 1in pressing contactfsurface'. 01 of the, contact button |05 against the bone structure, pushes the butt'on inwardly until the contact surface |01 is flush with 75 the adjacent supporting surface ||1 of the collar H6. This brings the armature |0| to its normal voperating position which. like in the modification described before, is just beyond, but close to, the freezing region, enabling transmission of a large vibratory power in a small size unit because of the relatively small gap. To prevent prolonged freezing of the armature to the pole surfaces |02 and |03, additional spacers |24,

like the spacers 13 in Figs. 3 and 4, are provided which prevent the armature from coming into contact with the pole faces and s'ecure immediate release of the vibratory diaphragm unit into its normal vibrating position upon the disappearance of the excessive ux.

Instead of using spacers for preventing prolonged freezing, the arrangement shown in Fig. 16 may be used, the button' being mounted within a collar H6 provided at its inner side with an inward projection` which limits the inwardA movement, like the arrangement of Fig. 9.

A vibrator so constructed will develop sufiicient .power for imparting intelligible sound impulses through the bone structure with a relatively small structure that permits its inconspicuous wear on the head f the user.I In general, such vibratorV may be madey within a size of 60 millimeters length, 30 millimeters height, and about 25 millimeters width.

The invention claimed in the present application is directed to the features of the bone conduction receiver disclosed in the various exemplifications described above.

The novel combination of a bone conduction receiver with coupling means for imparting hearing-inducing vibrations to the 'vertebrae of the spinal column of a deafened person so as to enable him to hear without making his impairment Yconspicuous is claimed in my copending application Serial No. 21,706, iled May 16, 1935`,-

i as a continuation in part, of the present application.

I claim: lIn a portable bone conduction hearing-aid de vice, an electromagnetic bone conduction receiver .of small size suitable for inconspicuous wear by the user comprising a magnetic core of substantial mass having a pole face, a casing enclosing said core, a magnetic armature resiliently supported by` said casing 'at a gap` `spacing of the order of 2 mils adjacent said pole face, windings interlinked with said corefor inducing in said gap magnetic forces imparting sound-frequency vibrations to said armature across said gap, a cover for said casing having an opening facing said armature, a contact member extending from said armature having an external contact surface projecting through said cover opening for engaging hearing-inducing bone structure of the user, and resilient supporting means for carrying said receiver in a iioating condition and pressing the contact surface of said contact member against hearing-inducing bone structure while said contact member is subjected to forces tendingto freeze said armature to said pole face, and means for adjustably locking said cover in a position at which the portion of the cover adjacent said opening limits the Vinwardmovement of said contact member to a position in which said lgap 

